Research activities at the USC Data Management Research Lab are focusing on the design and implementation of a High-performance Data Recording Architecture (HYDRA). The goal of HYDRA is to improve current and enable new applications by acting as an efficient media stream coordinator that manages the transmission, recording, and playback of many different data streams simultaneously. The objective of HYDRA is to use a unified paradigm that integrates multi-stream recording, retrieval and control in a synergetic manner. HYDRA aims to provide the same services for all media, independent of their bandwidth requirements, resolution or modality. One of the applications that we are exploring for this technology is a Distributed Immersive Performance where musicians and audiences are geographically disbursed in different locations.

HYDRA is capable of high definition live video streaming. We unveiled this feature on October 28, 2003. Video at 1280x720 pixel resolution (in HDV format) is transmitted at approximately 20 Mb/s over traditional IP networks such as the Internet. Each MPEG-2 transport stream video is acquired from a JVC JY-HD10U camera via FireWire, packetized, transmitted and displayed with a software or hardware decoder on Linux. Additionally, two audio channels are transmitted as well. In the past, achieving this level of media quality required very costly equipment. However, improvements in information technology now present us the opportunity to apply more cost-effective hardware and hence enable many more interesting applications.

The above image shows the pre-event tests of a 4-channel HYDRA live streaming setup that was used to stream The Miró Quartet: Live & Virtual for the Gala Event at the Fall 2004 Internet2 Member Meeting (Austin, Texas). Four HD cameras (on the right) are used to acquire live video which is then transmitted to and rendered on four receivers over a commodity IP network. (Note, no color calibration had been done at the time the picture was taken.)

The above images show our first long-distance test that was performed in January 2004 via a trans-pacific Internet2 link from the University of Hawaii at Honolulu, to the USC campus in Los Angeles, CA.

The above picture shows a trans-pacific, live two-way linkup between Inha University, Incheon, South Korea, and USC on October 8, 2004.

The above pictures show HD live streaming between two sites on the USC campus. Low latency rendering is achieved with an optimized software decoder that utilizes the MPEG decoding hardware-assistance available on recent graphics processing units (GPUs).

The HYDRA architecture is based on a scalable cluster design. Each cluster node is a off-the-shelf personal computer with attached storage devices and, for example, a Fast Ethernet connection. The HYDRA server software manages the storage and network resources to provide real-time service to the various clients that are requesting media streams.

Research Focus

The HYDRA project has motivated a number of different sub-projects that are aimed at improving various aspects of the system.

Admission Control: The task of the admission control algorithm is crucial to ensure that no more streams are admitted than the system can handle with a predefined quality. Unlike traditional data management systems, whose performance may degrade gracefully under high load conditions, streaming media servers experience undesirable stream disruptions (also called ``hiccups'') when resources are exhausted. The challenge of designing a good admission control algorithm is to allow the all resources to be utilized to their fullest potential while preventing overload conditions from occurring. The resources under consideration are (at least) main memory, processor utilization, effective disk and network bandwidth.

Memory Management: Managing the available memory efficiently is an important aspect of any multimedia streaming system. Main memory is required to temporarily hold data items while they are transferred between the incoming and outgoing network as well as the permanent disk storage. For efficiency reasons, network packets are generally much smaller than disk blocks. The assembly of incoming packets into data blocks and conversely the partitioning of blocks into outgoing packets requires main memory buffers. With a stream recorder, incoming data can be held in memory variable amount of time and the deadline by which a data block must be written to disk can be extended. This can reduce disk contention and hence the probability of stream disruptions.

Furthermore, HYDRA is the basis of the Distributed Immersive Performance (DIP) project. DIP is a testbed that integrates many of the technologies that are the result of multiple research efforts. The goal of the DIP is to reproduce the complete aural and visual ambience of an environment that includes people and other real and virtual elements.

We have performed experiments across both LAN and WAN environments. Our most recent tests were conducted via a trans-pacific Internet2 link from the University of Hawaii at Honolulu, to the USC campus in Los Angeles, CA.